Create a string that repeats itself x number of times

I want to create a function that returns a string a specific number of times. I have tried with this.

function stringRepeat(word, number) {
var string = ”” 
for(i= 0; i < number; i++) {
    string += word;
}
}
 console.log(stringRepeat("grey", 12));

However, it doesn´t do the job. What should I change?

I have tried to change ”string += word;” to ”console.log(word)” and then it executes (but i get the ”word” written on 12 different lines- I want to have it in one long string.)

When I execute the existing code I get ”undefined” as the result. Why is this?

Thanks in advance!